Endocardial Sarcoma, Rat. In: Jones TC, Mohr U, Hunt RD, editors. Cardiovascular and Musculoskeletal Systems. Berlin: Springer Berlin Heidelberg; 1991. pp. 56-62. [DOI: 10.1007/978-3-642-76533-9_11]

Pathology and incidence of amelanotic melanomas of the skin in F-344/N rats

A total of 121 spontaneous amelanotic melanomas of the skin were identified in 70 of 11,171 male and 51 of 10,927 female Fischer-344/N rats in 63 2-yr carcinogenicity studies conducted by the National Cancer Institute's Carcinogenicity Testing Program/National Toxicology Program. Amelanotic melanomas had characteristic anatomical locations and histologic features distinguishable from Schwann cell tumors. Of the 121 tumors, 84, 19, 10, and 8 cases occurred in the pinna, eyelid, scrotum, and perianal region (anus and tail), respectively. Amelanotic melanomas originated from the dermis and consisted of spindle cells arranged in an interlacing fascicular pattern often with a perivascular orientation; epithelioid cells were rarely seen. Only the tumors arising in the pinna metastasized to the lung and/or mandibular lymph nodes. The metastatic rate was 19% (16/84) of the tumors and was clearly increased with an increase in tumor size. Most metastasizing tumors had focal areas consisting of anaplastic spindle cells with an increased number of mitosis. The tumor cells stained positive for S-100 protein but negative for melanin. Ultrastructurally, the tumors were diagnosed as amelanotic melanomas based on the identification of numerous, intracytoplasmic premelanosomes without melanin formation in the tumor cells which were not enveloped by pericytoplasmic basal laminae. One localized amelanotic melanoma of the pinna was successfully transplanted to the subcutaneous tissue in the flank of 3 Fischer-344/N rats.

S-100 protein and glial fibrillary acidic protein (GFAP) in experimentally induced and spontaneous tumours of peripheral nerves in BDVI rats. Light microscopic and immunohistochemical study

Twenty-five ethylnitrosourea (ENU) induced and 24 spontaneous tumours of peripheral nerves as well as 28 spontaneous mesenchymal tumours in BDVI rats were studied by light microscopy and immunohistochemically for the presence of S-100 protein (S-100). Early ENU-induced schwannomas*) representing the thickenings of nerves showed weak or negative S-100 immunoreactivity. S-100 positivity (both in the cytoplasm and nucleus) was observed in all large ENU-induced tumours found in animals dying or killed at advanced age. Immunostaining was present in both cystic and solid areas of schwannomas. S-100 positivity was found in 20 of 24 spontaneous schwannomas: 14 of 20 positive tumours contained cysts. Twenty-seven schwannomas (12 ENU-induced and 15 spontaneous) were studied for the presence of glial fibrillar acid protein (GFAP) and 13 were positive (7 had cystic areas). GFAP-positivity was relatively high in 4 tumours (3 ENU-induced and 1 spontaneous); these tumours also showed intense S-100 reactivity. Immunoreactivity for S-100 occurred more frequently and was much more intense than that for GFAP. The incidence of spontaneous peripheral nerve tumours in BDVI males reached 4%, cystic schwannomas being the most frequent type. All spontaneous mesenchymal tumours except lipoma (S-100 positive) were negative for S-100 protein and for GFAP.